Modification of vacuum plasma sprayed tungsten coating on reduced activation ferritic/martensitic steels by friction stir processing

Tanigawa, Hiroyasu; Ozawa, Kazumi; Morisada, Yoshiaki*; Noh, S.*; Fujii, Hidetoshi*

Fusion Engineering and Design, 98-99, p.2080 - 2084, 2015/10

https://doi.org/10.1016/j.fusengdes.2015.04.059

The vacuum plasma spray (VPS) technique has been investigated as the most practical method to form Tungsten (W) layer as a plasma facing material in fusion devices. The issues are the thermal conductivity and the strength of VPS-W, i.e., the thermal conductivity of VPS-W were significantly lower than that of the bulk W, and the hardness of VPS-W is much less than that of the bulk W. These are mainly caused by the porous structure of VPS-W. In order to solve these issues, friction stir processing (FPS) was applied on VPS-W in this study. It was suggested that FSP can contribute to significant improvement both in mechanical and thermal properties of VPS-W coating.

Stress envelope of silicon carbide composites at elevated temperatures

Nozawa, Takashi; Kim, S.*; Ozawa, Kazumi; Tanigawa, Hiroyasu

Fusion Engineering and Design, 89(7-8), p.1723 - 1727, 2014/10

https://doi.org/10.1016/j.fusengdes.2013.12.032

A SiC/SiC composite is a promising candidate material for the advanced fusion DEMO blanket. For the design of the DEMO, the stability of high-temperature strength of SiC/SiC composites needs to be identified. Additionally, strength anisotropy needs to be clarified because of its unique fabric architecture. This study therefore aims to evaluate mechanical properties by various modes at elevated temperatures, eventually providing a stress envelope for the design. A P/W Tyranno-SA3 fiber reinforced CVI SiC matrix composite with multilayered SiC/PyC interface was evaluated in this study. Tensile and compressive tests were conducted by the SSTT specifically arranged for the high-temperature use. In-plane shear properties were contrarily estimated by the off-axial tensile method assuming that the mixed mode failure criterion is valid for composites. All tests were performed in vacuum. The preliminary test results indicate no degradation of both proportional limit stress (PLS) and the ultimate tensile strength at temperatures below 1000C. Similarly, no significant degradation of high-temperature compressive and in-plane shear properties were identified, finally providing the stress envelope at elevated temperatures for the design.

Characterization of failure behavior of silicon carbide composites by acoustic emission

Nozawa, Takashi; Ozawa, Kazumi; Tanigawa, Hiroyasu

Ceramic Materials for Energy Applications II, p.95 - 110, 2012/11

https://doi.org/10.1002/9781118217535.ch7

This study aims to identify failure behavior of SiC/SiC composites by varied test modes. For this purpose, acoustic emission (AE) was applied to detect composites' failure. Tensile and compressive tests were conducted for a plain-weave (P/W) chemical vapor infiltration (CVI) composite. Various loading angles were applied to discuss an anisotropic issue. AE results distinguished damage accumulation processes in axial and off-axial loading cases. Specifically, test results indicated a clear difference of damage density between tensile and compressive tests. This study also classified the characteristic failure modes by separately discussing localized variations of power within a time series by wavelet analysis.

Plan and reports of coupled irradiation (JRR-3 and JOYO of research reactors) and hot facilities work (WASTEF, JMTR-HL, MMF and FMF); R&D project on irradiation damage management technology for structural materials of long-life nuclear plant

Matsui, Yoshinori; Takahashi, Hiroyuki; Yamamoto, Masaya; Nakata, Masahito; Yoshitake, Tsunemitsu; Abe, Kazuyuki; Yoshikawa, Katsunori; Iwamatsu, Shigemi; Ishikawa, Kazuyoshi; Kikuchi, Taiji; et al.

JAEA-Technology 2009-072, 144 Pages, 2010/03

JAEA-Technology-2009-072.pdf:45.01MB

"R&D Project on Irradiation Damage Management Technology for Structural Materials of Long-life Nuclear Plant" was carried out from FY2006 in a fund of a trust enterprise of the Ministry of Education, Culture, Sports, Science and Technology. The coupled irradiations or single irradiation by JOYO fast reactor and JRR-3 thermal reactor were performed for about two years. The irradiation specimens are very important materials to establish of "Evaluation of Irradiation Damage Indicator" in this research. For the acquisition of the examination specimens irradiated by the JOYO and JRR-3, we summarized about the overall plan, the work process and the results for the study to utilize these reactors and some facilities of hot laboratory (WASTEF, JMTR-HL, MMF and FMF) of the Oarai Research-and-Development Center and the Nuclear Science Research Institute in the Japan Atomic Energy Agency.

Tensile and interfacial strength evaluation of SiC/SiC model composites

Ozawa, Kazumi; Nozawa, Takashi; Tanigawa, Hiroyasu

no journal, , 

Tensile and interfacial properties of unidirectional SiC/SiC model composites reinforced with Hi-Nicalon Type-S fibers with innermost pyrolytic carbon (PyC) layer thickness of 240 and 1150 nm (TypeS-240 and TypeS-1150, respectively) were evaluated by unloading/reloading cyclic tensile tests and single fiber push-out tests. Effective fiber bundle strength in the TypeS-240 and -1150 composites were 79-104% and 70-85%, compared with the original fiber bundle strength. According to the analytic results using hysteresis loops of tensile curves, interfacial sliding stress of the TypeS-1150 estimated to be about 0.7 times as large as the TypeS-240. This tendency was also confirmed by the single fiber push-out tests. These composites showed quasi-ductility, but it is considered that the composite with the thicker interphase could not achieve its fiber bundle strength, probably due to the lower interfacial sliding stress.

Microstructure investigation on SiC by nano-infiltration transient eutectic process after triple ion beam bombardment

Ozawa, Kazumi; Koyanagi, Takaaki*; Taguchi, Tomitsugu; Nozawa, Takashi; Tanigawa, Hiroyasu; Kondo, Sosuke*; Hinoki, Tatsuya*

no journal, , 

A SiC/SiC composite is a promising candidate functional/structural material for fusion DEMO reactor. To examine the effects of transmuted H mainly on microstructural cavity formation, the monolithic NITE-SiC with 6wt% YO-AlO sintering additive system were ion-irradiated to 10 dpa at 1000C nominally with 130 appmHe/dpa, and 40 or 400 appmH/dpa, respectively. In SiC grains, tiny cavities with 2 nm formed densely. However, it is revealed that H could not remarkably impact on cavity formation (size, density) in the condition studied. The influence of cavities formed along SiC-YAG grain boundary (GB) on cavity swelling seems to be also small, possibly attributed to its quite low density, even though the cavity size formed is three to five times larger than the size in CVI-SiC matrix in the same irradiation condition. Additional investigation of the microstructural evolution in YAG grain and SiC-YAG GB is a future plan.

Tensile and interfacial properties of unidirectional advanced SiC/SiC minicomposites

Ozawa, Kazumi; Nozawa, Takashi; Tanigawa, Hiroyasu; Kato, Yutai*; Snead, L. L.*

no journal, , 

A silicon carbide (SiC) matrix composite is a promising candidate for nuclear fusion energy applications. Unloading-reloading cyclic tensile tests were conducted to estimate interfacial properties for unidirectional SiC/SiC minicomposites reinforced by Hi-Nicalon Type-S (HNLS) or Tyranno-SA3 SiC fibers via CVI process were conducted. The interfacial properties were also evaluated by fiber push-out test. According to these results, it is implied that both fiber surface roughness and interfacial layter thickness can impact the tensile and interfacial properties.

Swelling of SiC and its helium effects for expected operating conditions based on some blanket designs using SiC materials

Ozawa, Kazumi; Nozawa, Takashi; Uto, Hiroyasu; Someya, Yoji; Tanigawa, Hiroyasu; Tobita, Kenji

no journal, , 

A silicon carbide fiber-reinforced silicon carbide matrix (SiC/SiC) composite is a promising candidate material for the advanced fusion DEMO blanket. Two options are considered for the use of the composites in the DEMO design: materials functionally used such as a flow channel insert in Pb-Li liquid cooling system, and ones used as a part of structural components. This paper primarily aims (1) to show examples of Japanese blanket concepts, such as SlimCS and VECTOR, which SiC materials are considered to be used, comparing with other US or EU designs, and (2) to summarize/organize the neutron/ion irradiated swelling data currently obtained for the target temperature ranges of mainly 700C for functional use and 1000C for structural, with a strong emphasis on the effects of helium on swelling of SiC.

Microstructural examination on nuclear grade SiC fibers after high dose ion-irradiation at FCI operation temperature region

Ozawa, Kazumi; Kondo, Sosuke*; Nozawa, Takashi; Tanigawa, Hiroyasu; Hinoki, Tatsuya*

no journal, , 

A SiC/SiC composite is a promising material for fusion DEMO reactor. In this presentation, dimensional and microstructural stabilities of advanced SiC fibers after high-dose ion irradiation at the temperature, where the composite is to be used as a flow channel insert (FCI), were evaluated by step height measurement and FE-TEM, respectively. As a preliminary result using the step height measurement, matrix and fiber was relatively flat and had no significant gap in a Tyranno-SA3 composite after ion irradiation at 600C to 100 dpa, while in a Hi-Nicalon Type-S composite a hollow part was observed in the center of the fiber. Differences of two types of advance SiC fibers on microstructure were discussed, compared with previous neutron/ion- irradiated data, considering the issues associated with ion irradiation and effects of pyloritic carbon interphase.

TEM characterization of advanced SiC fibers irradiated to high dose at relatively low temperature

Ozawa, Kazumi; Taguchi, Tomitsugu; Kurotaki, Hironori; Nozawa, Takashi; Tanigawa, Hiroyasu

no journal, , 

A silicon carbide (SiC) matrix composite is a promising candidate for nuclear fusion energy applications. In order to examine the dimensional stability and microstructure of two kinds of high purity and near stoichiometric SiC fiber (Hi-Nicalon Type-S and Tyranno-SA3) after irradiation, which contain impurities compared to high crystalline and stoichiometric -SiC matrix, self-ion irradiation experiments at relatively lower temperatures were performed at TIARA and DuET facility. The properties after the irradiation were evaluated by means of AFM for dimensional stability and FE-TEM for microscopy. After ion irradiation at 600C to 100 dpa, shrinkage of Hi-Nicalon Type-S was obtained but the degree was smaller than the case for the irradiation at 300C to 100 dpa. Contrarily, the shrinkage of Tyranno-SA3 fiber appeared to be much smaller than the Hi-Nicalon Type-S fiber after each irradiation condition.